Alignment of optical interfaces for data communication

ABSTRACT

An optical interface for data communication that can be manufactured and aligned in a cost effective manner includes an array of optical emitters and an optical receiver are positioned within a predetermined tolerance with reference to each other so as to establish an optical data communication path. To search for and determine which of the emitters of the array achieves the best alignment, the optical emitters are individually energized in a sequence, while monitoring the output signal of the optical receiver. For subsequent data communications, the optical emitter determined to achieve the best alignment is employed.

This application is a division of application Ser. No. 09/301,910, filedApr. 29, 1999, is now issued U.S. Pat. No. 6,272,271 which is herebyincorporated by reference in its entirety.

This invention was made with Government support under contract numberF33615-94-C-1531 awarded by DARPA. The Government has certain rights inthe invention.

BACKGROUND OF THE INVENTION

This invention relates generally to optical interfaces for datacommunication and, more particularly, to optical interfaces which can bemanufactured and aligned in a cost-effective manner, as well as tomethods for aligning such optical interfaces.

Optical data communications technology has a number of advantages overwire technology. For example, bandwidth, data rate and responsecharacteristics are superior to those of conventional wire technology.Optical technology is essentially immune to RFI (radio frequencyinterference) and EMI (electromagnetic interference) issues that plaguewire technology. Shielding as in coaxial cables is not required,allowing the overall size and weight of systems to shrink.

Optical fiber telephone lines and world wide data links are replacingthe bandwidth-limited wire technology. Likewise, optical technology,particularly optical interfaces for data communications, is highlydesired in a variety of applications such as multi-component modules(MCMs), various printed circuit board (PCB) technologies, and integratedbackplanes. Employing optical timing in radar transmit/receive modulesto form phased array antennas is an objective in design of radarinstallations.

In such systems, electro-optical devices can be employed at the point ofconversion from light to electronic transmission, and vice-versa. (Asemployed herein the term “light” is not limited to visible light, andincludes optical wavelengths both above and below the range of visiblelight wavelengths). Electro-optical devices typically comprisesemiconductor devices, which may be referred to as “chips” or “die”.Examples of optical emitters or transmitters include light emittingdiodes (LEDs), laser diodes, and arrays of these used in automobile taillight applications. An example of an optical receiver is a photodiode.The integration of such electro-optical devices within high densityinterconnect structures, including the use of adaptive lithographytechniques to produce optical interconnects, is disclosed inaforementioned Wojnarowski et al., U.S. Pat. Nos. 5,562,838 and5,737,458.

Problems associated with micro-optical alignment prevent the economicalusage of optical technology. Generally, micro-optical alignment is anexpensive hand tuning operation. Thus, what is limiting a great numberof potential applications is the ability to correctly align an opticaldie to an optical path, such as is represented by an optical fiber or bya corresponding optical die, as well as the ability to interconnect anoptical assembly to a backplane.

BRIEF SUMMARY OF THE INVENTION

In an exemplary embodiment of the invention, an array of opticalemitters, such as laser diodes or light emitting diodes (LEDs), forexample, and an optical receiver or an end of an optical fiber arepositioned within a predetermined tolerance with reference to each otherso as to establish an optical data communication path. One of theoptical emitters provides the most optimum path. To search for anddetermine which emitter in the array of optical emitters provides theoptimum optical path, that is, achieves the best alignment, the opticalemitters are individually energized in a sequence, while monitoring anoutput signal of the optical receiver or of the optical fiber. Thus, thelaser diode array, with redundant laser emitting cells, is energized ina scanning manner, while the receiver output signal is monitored for thebest fit signal response. This may be done individually in a sequentialmanner, or may be done automatically as various subassemblies areassembled into a system, and additionally upon each repair orreplacement operation. The scanning and monitoring may be performed by asetup align algorithm for post-assembly. For subsequent datacommunications, the optical emitter determined to achieve the bestalignment is employed.

Conversely, in another exemplary embodiment of the invention, an arrayof optical receivers and an optical emitter are mechanically positionedwithin a predetermined tolerance with reference to each other toestablish an optical data communication path. One of the opticalreceivers corresponds to the most optimum optical path from the opticalemitter. To determine which receiver in the array of optical receiverscorresponds to the most optimum optical path, in other words, whichachieves the best alignment, the optical emitter is energized, andoutput signals of the optical receivers are measured. For subsequentdata communications, the optical receiver determined to achieve the bestalignment is employed.

The invention accordingly provides optical-to-electronic interfaces in acost effective manner, and facilitates automating the alignment processbetween optical fibers, optical electronic assemblies, and opticalconnector interfaces to associated assemblies such as backplanes. Theinvention may be deployed in PC card and backplane assemblies, incombination with a variety of three-dimensional stacking technologies,and in a variety of other applications where critical alignment ofoptical subassemblies is important. The invention may also be employedto find related ends of long multi-fiber optical cables, such as underrivers and oceans. Labor intensive alignment operations are minimized ina manner suitable for production applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view depicting a printed circuit boardplugged into and optically coupled to a backplane array, with a portionof the backplane array cut away;

FIG. 2 is cross-sectional view taken on line 2—2 of FIG. 1;

FIG. 3 is a cross-sectional view taken on line 3—3 of FIG. 1;

FIG. 4 is a flow chart depicting a method embodying the invention;

FIG. 5 is a flow chart depicting an alternative method embodying theinvention;

FIG. 6 depicts two modules which may be part of a three-dimensionalstack of modules including optical interfaces embodying the invention;

FIG. 7 depicts an alternative three-dimensional stack of modulesembodying the invention;

FIG. 8 depicts yet another alternative three-dimensional stack ofmodules embodying the invention; FIG. 9 depicts a three-dimensionalstack of modules including optical interconnect ports in the sides ofthe modules and a corresponding array for data communications embodyingthe invention; and

FIG. 10 depicts an embodiment of the invention wherein an opticalconnection is aligned to an end of an optical fiber.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1, 2 and 3, schematically illustrated is aportion of a backplane array or card rack 20 receiving a plurality ofprinted circuit boards (PCBs), such as representative printed circuitboard 22. For electrical connections such as power and ground, printedcircuit board 22 includes finger-like electrical contacts 24 and 26 thatmate with corresponding contacts of a card edge connector 28, whichphysically is a part of backplane array 20. Representative componentsmounted to printed circuit board 22 are designated 30 and 32.Conventional structural support elements are omitted for clarity ofillustration. Thus, backplane array 20 is a conventional card rack thathas side shelf fixturing (not shown) for mechanical mounting and toalign the printed circuit board 22 for proper alignment of thefinger-like electrical contacts 24 and 26 with contacts of card edgeconnector 28.

For optical data communications, not subject to bandwidth, data rate andresponse characteristics of the card edge connector 28 and associatedfinger-like contacts 24 and 26, a two-dimensional array 36 of opticalemitters 38, such as LEDs or laser diodes, is mounted to printed circuitboard 22, and positioned within a predetermined tolerance with referenceto an optical receiver 40, such as a photodiode or other type ofphotodetector, for example, mounted to backplane array 20, so as toestablish an optical data communication path. Array 36 is large enoughto accommodate misalignment of array 36 with reference to opticalreceiver 40 within the predetermined tolerance. Arrow 42 represents abeam of light directed from one of the optical emitters 38 to opticalreceiver 40. A lens (not shown) may be employed to focus the light.

Optical emitters 38 comprising array 36 are packaged in any suitablemanner. The packaging pitch of optical emitters 38 determines a minimumtolerance. LEDs and multiplexing circuitry may be included on the samewafer scale integration (WSI) chip. In one embodiment, array 36comprises an application specific integrated circuit (ASIC) chipincluding the optical emitters. The embodiment permits a tight packagingpitch and provides a good tolerance for alignment with the opticalreceiver.

High density interconnect (HDI) fabrication techniques, as are disclosedin Eichelberger et al., U.S. Pat. No. 4,783,695 and in commonly assignedWojnarowski et al., U.S. application Ser. No. 09/258,935, filed Mar. 1,1999, entitled “Light Source Including an Array of Light EmittingSemiconductor Devices and Control Method”, can be used instead of or inaddition to an ASIC chip This results in tighter packaging compared tothe use of wire bonding. A micro PCB with wire bonds can also be used.

For alignment purposes, optical emitters 38 are individually energizedin a sequence, while the output signal of optical receiver 40 ismonitored, to determine which emitter 38 in the array 36 of emittersachieves the best optical alignment, which may be referred to as themost optimum available optical path. Thereafter, for subsequent datacommunications, the particular one of the optical emitters 38 determinedto achieve the best alignment is employed.

A typical alignment process embodying the invention is represented inthe flow chart of FIG. 4 which in one embodiment may be embodied in acontroller 51 comprising a computer or microprocessor, for example.During the alignment process individual emitters 38 of array 36 areaddressed in any conventional manner, typically by multiplexing. Thus,in box 50 a first one of the emitters 38 is energized. The resultantoutput signal (if any) of receiver 40 is stored to initialize a variableBEST_SIGNAL_SO FAR, and an identification of the particular emitter 38is stored to initialize another variable BEST_EMITTER_SO_FAR.

A loop is then entered, beginning with box 52, wherein the next emitter38 in a sequence is energized. In decision box 54, the output signal (ifany) of receiver 40 is compared with the value of the stored variableBEST_SIGNAL_SO_FAR. If the receiver output signal is greater than thevalue of the stored variable BEST_SIGNAL_SO_FAR, then in box 56 thereceiver 40 output signal is stored as the new value of the variableBEST_SIGNAL_SO_FAR, and the identification of the particular one of theemitters 38 is stored as the new value of the variableBEST_EMITTER_SO_FAR. Execution then proceeds to decision box 58. If, onthe other hand, in decision box 54 the receiver 40 output signal is lessthan or equal to the value of the variable BEST_SIGNAL_SO_FAR, thenexecution proceeds directly to decision box 58.

Decision box 58 determines whether the scanning process is completed. Ifthe last emitter 38 in the sequence has not been energized, thenexecution loops back to box 52. If the last emitter 38 has beenenergized, then decision box 60 next determines whether a suitableoptical alignment or “fit” has been achieved. Thus if in decision box 60it is determined that the magnitude of the receiver 40 output signalstored as the value of the variable BEST_SIGNAL_SO_FAR is insufficient,indicating that satisfactory alignment has not been achieved, then inbox 62 relevant components (e.g. printed circuit board 22) arere-seated, and the process begins again with box 50. If in decision box60 it is determined that satisfactory alignment has been achieved, thenexecution proceeds to box 64, where in the particular emitter 38 whichachieved the best alignment as identified in the variableBEST_EMITTER_SO_FAR is employed for subsequent data communications.

The alignment process represented in FIG. 4 may be done manually by atechnician, or may be accomplished as an electronically-directedautomatic alignment process, either on a full time basis, or for aone-time-then-stop alignment. Alignment is typically performed duringinitial assembly of a system, as well as upon each repair or replacementoperation, such as when card 22 is removed and then replaced.

Moreover, in environments that are particularly prone to alignmentdegradation, such as where vibration or dirt is present, the automaticalignment process may be performed periodically. The automatic periodicalignment may be a dynamic process which in effect optimizes the opticalpath on an essentially continuous basis. Duty cycles are such thatmultiplexing can be employed to transmit data between emitter energizingpulses which are for alignment purposes. Such is particularlyadvantageous where vibration or other environmental factors are present.

Although array 36 of optical emitters 38 is shown mounted to printedcircuit board 22 and optical receiver 40 is shown mounted to backplane20 for optical data transmission from printed circuit board 22 tobackplane 20, the relative positions of emitter array 36 and receiver 40may be reversed for optical data transmission from backplane 20 toprinted circuit board 22, with receiver 40 in that case being mounted onprinted circuit board 22 and array 36 of emitters 38 carried bybackplane 20. Further, for bidirectional optical data transmission fromprinted circuit board 22 to backplane 20 as well as from backplane 20 toprinted circuit board 22, an array 36 of optical emitters 38 and anoptical receiver 40 in that case may be mounted on each of the printedcircuit board 22 and backplane 20.

In a converse configuration embodying the invention, a single opticalemitter may be employed in conjunction with an array of opticalreceivers. Such a configuration would be illustrated in FIGS. 1-3 bysubstituting for element 40 an optical emitter such as a laser diode oran LED, and substituting for element 36 an array of optical receivers,such as photodiodes or other types of photodetectors, for example.Lensing (not shown) may be used to optimize the light path. Whether toemploy a single optical receiver and an array of optical emitters, or asingle optical emitter and an array of optical receivers is determinedby a variety of decision factors, such as component cost and size. Asdiscussed above, an optical device array may be optimized using customASIC (application specific integrated circuit) technology with thedesired minimum pitch for alignment, with multiplexing circuitryincluded on the same device, if desired. Again, the relative positionsof elements 36 and 40 may be reversed, for either optical datatransmission from printed circuit board 22 to backplane 20 or opticaldata transmission from backplane 20 to printed circuit board 22.Bi-directional optical data transmission in the converse configurationmay be accomplished by mounting an array of optical receivers and anoptical emitter on each of the printed circuit board 22 and backplane20.

FIG. 5 represents steps of an alignment process embodying the inventionwhere the converse configuration of a single optical emitter and anarray of optical receivers is employed. In one embodiment, the flowchartof FIG. 5 may be embodied in a controller 71 comprising a computer ormicroprocessor, for example The output signals of individual receiversin the array are addressed in a suitable manner, such as bymultiplexing. Thus, in box 70 the emitter is energized. In box 72, theoutput signal of the first receiver in a sequence is measured, andstored to initialize the variable BEST_SIGNAL_SO_FAR, and anidentification of the receiver is stored to initialize the variableBEST_RECEIVER_SO_FAR.

Next, a loop is entered beginning with box 74, wherein the output signalof the next receiver in the sequence is measured. In decision box 76,this receiver output signal is compared to the value of the storedvariable BEST_SIGNAL_SO_FAR. If the receiver output signal is greaterthan the value of the variable BEST_SIGNAL_SO_FAR, then in box 78 thereceiver output signal is stored as the new value for the variableBEST_SIGNAL_SO_FAR, and the identification of the particular receiver isstored as the new value of the variable BEST_RECEIVER_SO_FAR. Executionthen proceeds to decision box 80. If, on the other hand, in decision box76 it is determined that the current receiver output signal is less thanor equal to the value stored in variable BEST_SIGNAL_SO_FAR, thenexecution proceeds directly to decision box 80.

In decision box 80, it is determined whether the loop is completed. Ifin decision box 80 it is determined that the last emitter has not beenprocessed, then execution proceeds back to box 74. If, on the otherhand, the last receiver output signal has been scanned, decision box 82next determines whether a suitable optical alignment or “fit” has beenachieved. Thus if in decision box 82 it is determined that the magnitudeof the receiver output signal stored as the value of the variableBEST_SIGNAL_SO_FAR is insufficient, indicating that satisfactoryalignment has not been achieved, then in box 84 relevant components,such as a printed circuit board, are re-seated, and the process beginsagain with box 70. If in decision box 82 it is determined thatsatisfactory alignment has been achieved, then in box 86 the particularreceiver identified as having the BEST_SIGNAL_SO_FAR is employed forsubsequent data communications.

Similarly to what is described above with reference to FIG. 4, thealignment process represented in FIG. 5 may be performed eithermanually, such as by a technician, or as an electronically-directedautomatic alignment process. The alignment process may be performed uponinitial assembly, subsequent repairs, or periodically, which mayapproach a continuous dynamic process, particularly in environmentswhere vibration or other environmental factors are present.

Referring next to FIG. 6, represented in highly schematic form is athree-dimensional stack 90 of modules, comprising representativemulti-chip modules (MCMs) 92 and 94. By way of example, each of the MCMs92 and 94 has been manufactured employing high density interconnect(HDI) fabrication techniques, such as are disclosed in aforementionedEichelberger et al., U.S. Pat. No. 4,783,695. Alternatively, stack 90may comprise stacked printed circuit boards (PCBs). Such a stack 90 canbe disassembled for repair or reconfiguration as required, and thenre-assembled.

Very briefly, in systems employing an high density interconnect (HDI)structure, a ceramic substrate is provided, and individual cavities orwells having appropriate depths at the intended locations of the variouschips, are prepared, or one large cavity. Various components are placedin their desired locations within the cavities and adhered to thesubstrate by means of a thermoplastic adhesive layer. Alternatively themolded substrate technique disclosed in Fillion et al., U.S. Pat. No.5,353,498 may be employed, or the flexible structure disclosed inEichelberger et al., U.S. Pat. No. 5,452,182.

A multilayer high density interconnect (HDI) overcoat structure is thenbuilt up to electrically interconnect the components. To begin the HDIovercoat structure, a polyimide dielectric film, such as KAPTON®polyimide film (KAPTON is a trademark of DuPont Co.), about 0.0005 and0.003 inch (12.5 to 75 microns) thick is pretreated to promote adhesionand coated on one side with ULTEM® polyetherimide resin (ULTEM is atrademark of General Electric Co.), or another thermoplastic, andlaminated across the tops of the chips, other components and thesubstrate, with the ULTEM® resin serving as a thermoplastic adhesive tohold the KAPTON® film in plate. Exemplary lamination techniques aredisclosed in Eichelberger et al., U.S. Pat. No. 4,933,042.

The actual as-placed locations of the various components and contactpads thereon are typically determined by employing optical imagingtechniques. Via holes are adaptively laser drilled in the KAPTON filmand ULTEM adhesive layers in alignment with the contact pads on theelectronic components in their actual as-placed portions. Exemplarylaser drilling techniques are disclosed in Eichelberger et al., U.S.Pat. Nos. 4,714,516 and 4,894,115, and Loughran et al., U.S. Pat. No.4,764,485.

A metallization layer is deposited over the KAPTON film layer andextends into the via holes to make electrical contact to the contactpads disposed thereunder. This metallization layer may be patterned toform individual conductors during its deposition, or may be deposited asa continuous layer and then patterned using photoresist and etchingtechniques. The photoresist is preferably exposed under a laser which,under program control, is scanned relative to the substrate to providean accurately aligned conductor pattern upon completion of the process.Exemplary technique for patterning the metallization layer are disclosedin Wojnarowski et al., U.S. Pat. Nos. 4,780,177 and 4,842,677, andEichelberger et al., U.S. Pat. No. 4,835,704. Any misposition of theindividual electronic components and their contact pads is compensatedfor by an adaptive laser lithography system as disclosed inaforementioned U.S. Pat. No. 4,835,704.

In the particular embodiment of FIG. 6, only the electronic componentscomprising electro-optical devices included in modules 92 and 94 fordata communications are illustrated, and remaining electronic componentsincluded in modules 92 and 94 are omitted for clarity of illustration.

Modules 92 and 94 have respective facing portions 96 and 98, whichillustratively are the bottom of module 92 and the top of module 94. Thedistance between modules 92 and 94 is exaggerated in FIG. 6 for purposesof illustration, and mechanical mounting details are omitted.

Upper module 92 comprises a substrate 100 having a substrate surface 102and a cavity or well 104 containing an optical receiver 106 in the formof a semiconductor die having an active major surface 108. On activemajor surface 108 are a receive sense area 110, and a received signalcontact pad 112.

Cavity 104 is metallized, and has an electrically conductivemetallization layer 114 extending to a contact pad 116 on surface 102 ofsubstrate 100. Receiver die 106 has a metallized back contact 118 inelectrical contact with cavity 104 metallization 114, and securedemploying solder or an electrically conductive adhesive so as toestablish electrical contact.

To provide electrical connections, an HDI overcoat layer 120 includes anoptically transparent dielectric film 122 laminated over surface 102 ofsubstrate 100 and active major surface 108 of receiver die 106, andadhered employing an optically transparent thermoplastic adhesive layer124. Optionally a window (not shown) may be formed in polyimide 122 andadhesive 124 layers over receive sense area 1 10. Such a window can beformed by laser ablation, with or without a mask. Suitable techniquesare disclosed in aforementioned Eichelberger et al., U.S. Pat. No.4,894,115; Cole et al., U.S. Pat. No. 5,169,678; Kornrumpf et al., U.S.Pat. No. 5,157,255; and Wojnarowski et al., U.S. Pat. No. 5,302,547.

Vias 126 and 128 are formed through dielectric film layer 122 andadhesive layers 124 in alignment with well metallization contact pad 116and with signal contact pad 112, respectively. Conductors 130 and 132comprising a patterned metallization layer extend from vias 126 and 128to representative module contact pads 134 and 136, respectively.

In a similar manner, lower module 94 comprises a substrate 140 having asubstrate surface 142 and a metallized cavity or well 144 containing anoptical transmitter 146 in the form of a semiconductor die having anarray 148 of optical emitters 152, such as LEDs or laser diodes at anactive major surface 154. On active major surface 154 is arepresentative electrical contact 156, which serves a control input forcontrolling activation of individual emitters 152 of array 148. An arrow157 represents light (not necessarily visible light) from emitter 152 ofarray 148 directed towards receive sense area 110.

Optical transmitter die 146 includes a metallized back contact 158secured to and electrically connected to a metallization layer 160within cavity 144, and extending to a contact pad 162 on substrate 140surface 142.

For electrical interconnections, an HDI overcoat layer 164 includes anoptically transparent dielectric film 166 laminated over substrate 140surface 142 and active major surface 154, employing an adhesive layer168. Representative vias 170 and 172 are formed over contact pads 162and 156, and representative electrical conductors 174 and 176 comprisinga patterned metallization layer extend from vias 170 and 172 torepresentative module contact pads 178 and 180, respectively. Optionallya window (not shown) may be formed in polyimide 166 and adhesive 168layers over array 148 of emitters 152.

Upon assembly of stack 90, optical emitter array 148 and receive sensearea 110 are positioned within a predetermined tolerance of each otherto establish an optical data communication path. Array 148 is largeenough to accommodate misalignment of array 148 and receive sense area110 with reference to each other within the predetermined tolerance. Thesizes of emitters 152 and receive sense area 110 are preferablyoptimized.

During the actual alignment process, optical emitter array 148 andreceive sense area 110 of FIG. 6 are operated in the same manner as isdescribed hereinabove with reference to FIGS. 1-4 to identify which oneof the individual optical emitters 152 provides the optimum datacommunication path for transmitting signals from lower module 94 toupper module 92. The particular emitter 152 so identified is employedfor subsequent data communications.

Although array 148 of optical emitters 152 is shown on lower module 94and optical receiver 110 is shown on upper module 92 for optical datatransmission from lower module 94 to upper module 92, the relativepositions can be reversed for optical data transmission from uppermodule 92 to lower module 94. For bi-directional optical datatransmission, an array 148 of optical emitters 152 and an opticalreceiver 110 can be mounted on each of the modules 92 and 94.

In a converse configuration, rather than having an array 148 of emitters152 and a single optical receiver 110, a single emitter may be employedin combination with an array of receivers. In such converseconfiguration, element 110 would comprise an optical emitter, element148 would comprise an array of optical receivers, and the direction ofarrow 157 would be reversed.

Referring next to FIG. 7, depicted is another three-dimensional stack200 of MCMs 202, 204 and 206. Alternatively, stack 200 may comprisestacked PCBs or stacked semiconductor wafers. In overview, FIG. 7illustrates an embodiment in which the electro-optical devices arelocated on the tops 208, 210 and 212 of the individual modules 202, 204and 206, facilitated by -employing optical waveguides 214 and 216 and,in addition, in which an intermediate module, such as module 204,includes both optical transmit and optical receive elements.

In the module stack 200 of FIG. 7, the lowermost module 206 iscomparable to module 94 of FIG. 6. Module 206 comprises a substrate 220having a substrate surface 222 and a metallized cavity or well 224containing an optical transmitter 226 in the form of a semiconductor diehaving an array 228 of optical emitters 230, such as LEDs or laserdiodes at an active major surface 232. On active major surface 232 is arepresentative electrical contact 234, which serves a control input forcontrolling activation of individual emitters 230 of array 228. An arrow236 represents light (not necessarily visible light) from 10 an emitter230 of array 228 directed towards intermediate module 204.

Optical transmitter die 226 includes a metallized back contact 238secured to and electrically connected to a metallization layer 240within cavity 224, and extending to a contact pad 242 on substrate 220surface 222.

For electrical interconnections, an HDI overcoat layer 244 includes anoptically transparent dielectric film 246 laminated over substrate 220surface 222 and active major surface 232, employing an adhesive layer248. Representative vias 250 and 252 are formed over contact pads 242and 234, and representative electrical conductors 254 and 256 comprisinga patterned metallization layer extend from vias 250 and 252 torepresentative module contact pads 258 and 260, respectively. Optionallya window (not shown) may be formed in polyimide 166 and adhesive 168layers over array 228 of emitters 230.

In the module stack of 200 of FIG. 7, intermediate module 204 comprisesa substrate 270 having a substrate surface 272 and two metallizedcavities or wells 274 and 276 respectively containing an opticaltransmitter 278 in the form of a semiconductor die having an array 280of optical emitters 282, such as LEDs or laser diodes at an active majorsurface 284; and an optical receiver 286 in the form of a semiconductordie having a receive sense area 288 on an active major surface 290. Onactive major surface 284 of transmitter die 278 is a representativeelectrical contact 292 which serves as a control input for controllingactivation of individual emitters 282 of array 280. Also on active majorsurface 290 of optical receiver die 286 is a received signal contact pad294. An arrow 296 represents light (not necessarily visible light) froman emitter 282 of array 280 directed towards upper module 202.

Optical transmitter die 278 includes a metallized back contact 298secured to and electrically connected to a metallization layer 300within cavity 274, and extending to a contact pad 302 on substrate 270surface 272. In the same manner, optical receiver die 286 includes ametallized back contact 304 secured to and electrically connected to ametallization layer 306 within cavity 276, and extending to a contactpad 308 on substrate 270 surface 272.

For electrical interconnections, an HDI overcoat layer 312 includes anoptically transparent dielectric film 314 laminated over substrate 270surface 272 and active major surfaces 284 and 290 of die 278 and 286,employing an adhesive layer 316. For electrical connections totransmitter die 278, representative vias 318 and 320 are formed overcontact pads 284 and 302, and representative electrical conductors 322and 324 extend from vias 318 and 320 to representative module contactpads 326 and 328, respectively. For electrical connections to receiverdie 286, representative via holes 330 and 332 are formed over contactpads 294 and 308, and representative electrical conductors 334 and 336comprising part of the same patterned metallization layer as conductors322 and 324 extend from vias 330 and 332 to representative modulecontact pads 338 and 340, respectively. Optionally a window (not shown)may be formed in polyimide 314 and adhesive 316 layers at least overarray 280 of emitters 282.

To provide a path for laser or LED light represented by arrow 236 fromone of the emitters 230 of array 238 of lower module 206 to receivesense area 288 of receiver die 286 of intermediate module 204, waveguide216 is positioned generally on top 210 of module 204, with an end 342 ofwaveguide 216 positioned over receive sense area 288 so that opticalsignals presented to the other end 344 of waveguide 216 are directed toreceive sense area 288. An aperture 346 is formed through module 204substrate 270 and positioned so as to provide an optical path from array238 to waveguide end 344. To achieve a minimum loss configuration,particularly in view of beam divergence, the beam of laser or LED lightrepresented by arrow 236 may need to be guided along part or all of theoptical path. For example, optical fibers (not shown) may be insertedthrough aperture 346.

Example waveguide materials include glass and sufficiently transparentpolymer materials, for example. Methods for making optical waveguidesare disclosed in Wojnarowski et al., U.S. Pat. Nos. 5,525,190, 5,562,838(aforementioned) and 5,737,458 (aforementioned). Laser machining can beemployed to form internally reflective bevels on waveguides 214 and 216.

The uppermost module 202 in module stack 200 of FIG. 7 comprises asubstrate 360 having a substrate surface 362 and a metallized cavity orwell 364 containing an optical receiver 366 in the form of asemiconductor die having a receive sense area 368 on an active majorsurface 370. Also on active major surface 370 is a representativeelectrical contact pad 372, which serves as a received signal contactpad 372. Optical receiver die 366 includes a metallized back contact 374secured to and electrically connected to a metallization layer 376within cavity 364, and extending to a contact pad 378 on substrate 360surface 362.

For electrical interconnections, an HDI overcoat layer 380 includes anoptically transparent dielectric film 382 laminated over substrate 360surface 362 and active major surface 370, employing an adhesive layer384. Representative vias 386 and 388 are formed over contact pads 372and 378, and representative electrical conductors 390 and 392 comprisinga patterned metallization layer extend from vias 386 and 388 torepresentative module contact pads 394 and 396, respectively.

To provide a path for laser or LED light represented by arrow 296 fromone of the emitters 282 of array 280 of intermediate module 204 toreceive sense area 368 of receiver die 366 of upper module 202,waveguide 214 is positioned generally on top 208 of module 202, with anend 398 of waveguide 214 positioned over receive sense area 368 so thatoptical signals presented to the other end 400 of waveguide 214 aredirected to receive sense area 368. An aperture 402 is formed throughmodule 202 substrate 360 and positioned so as to provide an optical pathfrom array 280 to waveguide end 400. To achieve a minimum lossconfiguration, particularly in view of beam divergence, the beam oflaser or LED light represented by arrow 296 may need to be guided alongpart or all of the optical path. For example, optical fibers (not shown)may be inserted through aperture 402.

Although apertures 346 and 402 through substrates 270 and 360 areillustrated, an alternative is to employ transparent substrates 270 and360, for example made of silicon, quartz or sapphire, in conjunctionwith light transmission of an appropriate wavelength. For example,silicon is transparent to light at a wavelength of approximately 1000nm.

Upon assembly of the FIG. 7 module stack 200, optical emitter array 228of lower module 206 and receive sense area 288 of intermediate module204 are in general positioned within a predetermined tolerance withreference to each other so as to establish an optical data communicationpath. More particularly, optical emitter array 228 is positioned withreference to aperture 346 leading to waveguide 216 end 344. Emitterarray 228 is large enough to accommodate misalignment within thepredetermined tolerance. Likewise, optical emitter array 280 ofintermediate module 204 and receive sense area 368 of upper module 202are in general positioned within a predetermined tolerance withreference to each other so as to establish an optical data communicationpath. More particularly, optical emitter array 280 is positioned withreference to aperture 402 leading to waveguide 214 end 400. Emitterarray 280 is large enough to accommodate misalignment within thepredetermined tolerance.

During the actual alignment process, optical emitter array 228 andreceive sense area 288 of FIG. 7, as well as optical emitter array 280and receive sense area 368, are operated in the same manner as isdescribed hereinabove with reference to FIGS. 1-4, to identify which oneof the individual optical emitters 230 of array 228 provides the optimumdata communication path for transmitting signals from lower module 206to intermediate module 204, and to identify which one of the individualoptical emitters 282 of array 280 provides the optimum datacommunication path for transmitting signals from intermediate module 204to upper module 202. The particular emitter 230 and the particularemitter 282 so identified are employed for subsequent datacommunications.

FIG. 8 depicts an alternative module stack 420 of MCMs 422, 424 and 426.Module stack 420 of FIG. 8 may be viewed as embodying an optical dataconfiguration which is the converse of the configuration of module stack200 of FIG. 7, in that the optical receiver elements are organized asarrays, and the optical transmitter elements are single-emitterelements. As in FIG. 7, in FIG. 8 all electro-optical devices arelocated on the tops 428, 430 and 432 of the individual modules 422, 424and 426, facilitated by employing optical waveguides 428 and 430. Inaddition, optically transparent module substrates are employed. Thusmodules 422, 424 and 426 comprise respective substrates 432, 434 and436, and at least substrates 432 and 434 are transparent at the opticalwavelengths employed for data communications. Also, an intermediatemodule, such as module 424, includes both optical transmit and opticalreceive elements.

In the module stack 420 of FIG. 8, substrate 436 of module 426 has asubstrate surface 438 and a metallized cavity or well 440 containing anoptical transmitter 442 in the form of a semiconductor die comprising anoptical emitter 444, such as an LED or laser diode, at an active majorsurface 446. Also on active major surface 446 is a representativeelectrical contact 448, which serves a signal input for activatingemitter 444. An arrow 450 represents light (not necessarily visiblelight) from emitter 444 directed towards intermediate module 424.

Optical transmitter die 442 includes a metallized back contact 452secured to and electrically connected to a metallization layer 454within cavity 440, and extending to a contact pad 456 on substrate 436surface 438.

For electrical interconnections, an HDI overcoat layer 458 including anoptically transparent dielectric film 460 laminated over substrate 436surface 438 and active major surface 446, employing an adhesive layer462. Representative vias 464 and 466 are formed over contact pads 456and 448, and representative electrical conductors 468 and 470 comprisinga patterned metallization layer extend from vias 464 and 466 torepresentative module contact pads 472 and 474, respectively. Optionallya window (not shown) may be formed in polyimide 460 and adhesive 462layers over optical emitter 444.

Optically transparent substrate 434 of intermediate module 424 has asubstrate surface 482 and two metallized cavities or wells 484 and 486respectively containing an optical transmitter 488 in the form of asemiconductor die having an optical emitter 490, such as LEDs or laserdiodes at an active major surface 492; and an optical receiver array inthe form of a semiconductor die 494 having an array 496 of opticalreceiver elements 498 on an active major surface 500. On active majorsurface 492 of transmitter die 488 is a representative electricalcontact 502 which serves as a signal input for activating emitter 490.Also on active major surface 500 of optical receiver die 486 is arepresentative signal contact pad 504 for selection of and readingoutput signals from individual ones of receiver elements 498 of array496. An arrow 506 represents light (not necessarily visible light) fromemitter 490 directed towards upper module 422.

Optical transmitter die 488 includes a metallized back contact 508secured to and electrically connected to a metallization layer 510within cavity 484, and extending to a contact pad 512 on substrate 434surface 482. In the same manner, optical receiver die 494 includes ametallized back contact 514 secured to and electrically connected to ametallization layer 516 within cavity 486, and extending to a contactpad 518 on substrate 434 surface 482.

For electrical interconnections, an HDI overcoat layer 522 includes anoptically transparent dielectric film 534 laminated over substrate 434surface 482 and active major surfaces 492 and 500 of die 488 and 494,employing an adhesive layer 536. For electrical connections totransmitter die 488, representative vias 538 and 540 are formed overcontact pads 502 and 512, and representative electrical conductors 542and 544 extend from vias 538 and 540 to representative module contactpads 546 and 548, respectively. For electrical connections to receiverdie 494, representative vias 550 and 552 are formed over contact pads504 and 518, and representative electrical conductors 554 and 556comprising part of the same patterned metallization layer as conductors542 and 544 extend from vias 542 and 544 to representative modulecontact pads 558 and 560, respectively. Optionally a window (not shown)may be formed in polyimide 534 and adhesive 536 layers at least overemitter 490.

To provide a path for laser or LED light represented by arrow 450 fromemitter 444 on lower module 426 to receiver array 496 on die 494 ofintermediate module 424, waveguide 430 is positioned generally on top430 of module 424, with an end 562 of waveguide 430 positioned overreceiver array 496 so that optical signals presented to the other end564 of waveguide 430 are directed to receiver array 564. Since substrate434 is optically transparent, light 450 from emitter 444 passes throughsubstrate 434 to waveguide 430 end 564.

The uppermost module 422 in module stack 420 of FIG. 8 has a substratesurface 572 and a metallized cavity or well 574 containing an opticalreceiver array in the form of a semiconductor die 576 having an array578 of optical receiver elements 580 on an active major surface 582.Also on active major surface 582 is a representative electrical contactpad 584 for selection of and reading output signals from individual onesof receiver elements 580 of array 578. Optical receiver die 576 includesa metallized back contact 586 secured to and electrically connected to ametallization layer 588 within cavity 574 and extending to a contact pad590 on substrate 432 surface 572.

For electrical interconnections, an HDI overcoat layer 592 includes anoptically transparent dielectric film 592 laminated over substrate 432surface 572 and active major surface 582, employing an adhesive layer596. Representative vias 598 and 600 are formed over contact pads 584and 590, and representative electrical conductors 602 and 604 comprisinga patterned metallization layer extend from vias 598 and 600 torepresentative module contact pads 606 and 608, respectively.

To provide a path for laser or LED light represented by arrow 506 fromemitter 490 on intermediate module 204 to receiver array 578 on die 576of upper module 422, waveguide 428 is positioned generally on top 428 ofmodule 422, with an end 610 of waveguide 428 positioned over receiverarray 578 so that optical signals presented to the other end 610 ofwaveguide 428 are directed to receiver array 578. Since substrate 432 isoptically transparent, light 506 from emitter 490 passes throughsubstrate 432 to waveguide 428 end 610.

Upon assembly of the FIG. 8 module stack 420, optical emitter 444 oflower module 426 and receiver array 496 of intermediate module 424 arein general positioned within a predetermined tolerance with reference toeach other so as to establish an optical data communication path. Moreparticularly, optical emitter 444 is positioned with reference tosubstrate 434 and waveguide 430 end 564. Receiver array 496 is largeenough to accommodate misalignment within the predetermined tolerance.Likewise, optical emitter 490 of intermediate module 424 and receiverarray 578 of upper module 422 are in general positioned within apredetermined tolerance with reference to each other so as to establishan optical data communication path. More particularly, optical emitter490 is positioned with reference to substrate 432 and waveguide 428 end610. Receiver array 578 is large enough to accommodate misalignmentwithin the predetermined tolerance.

During the actual alignment process, optical emitter 444 and receiverarray 496 of FIG. 8, as well as optical emitter 490 and receiver array578, are operated in the same manner as is described hereinabove withreference to FIGS. 1-3 and 5, to identify which one of the individualoptical receivers 498 of array 496 provides the optimum datacommunication path for transmitting signals from lower module 426 tointermediate module 424, and to identify which one of the individualoptical receivers 580 of array 578 provides the optimum datacommunication path for transmitting signals from intermediate module 424to upper module 422. Thus optical emitter 444 is energized and theoutput signals of the individual receivers of array 496 are measured,and optical emitter 490 is energized and the output signals of theindividual receivers of array 578 are measured. The particular receiver498 and the particular receiver 580 so identified are employed forsubsequent data communications.

Referring next to FIG. 9, illustrated is yet another three dimensionalstack 600 of MCMs 602, 604 and 606 shown assembled by means of screws608 and 610 and a pressure plate 612 to a base 614. An example of such amodule stack 600 is a stack of PCBs, MCMs or the like, separated byz-axis interposer material which is electrically conductive in only onedirection, and pressed together. Stacks of stacks may also be assembled,employing the stack structure of Eichelberger et al., U.S. Pat. No.5,019,946.

As an embodiment of the invention, modules 602, 604 and 606 have opticalreceivers 630, 632, 634, 636, 638 and 640 in the sides of the module602, 604 and 606. These optical receivers 630, 632, 634 636, 638 and 640may also be viewed as optical pins or ports, and may also comprise theends of optical fibers or waveguides.

Either individual smaller arrays (not shown) of optical emitters, or asingle relatively larger array 644 of optical emitters 646 is positionedwithin a predetermined tolerance with reference to the optical receiver632, 634, 636, 638 and 640 for establishing optical data communicationspath to the module 602, 604 and 606.

During the actual alignment process, optical emitter array 644 and theindividual optical receivers 630, 632, 634, 636, 638 and 640 areoperated in the same manner as is described hereinabove with referenceto FIGS. 1-4 to identify which one of the individual optical emitters646 of array 644 provides the optimum data communication path fortransmitting signals from array 644 to each of the optical receivers630, 632, 634, 636, 638 and 640. A different one of the individualoptical emitters 646 is so identified for optical data communicationswith each of the optical receivers 630, 632, 634, 636, 638 and 640.

FIG. 10 depicts an embodiment wherein an array 700 of optical emitters702, such as LEDs or laser diodes, and an end 704 of an optical fiber706 are aligned with reference to each other. At the other end 708 ofoptical fiber 706 is an optical signal receiver 710. Receiver 710 cancomprise a semiconductor die, or a camera, for example.

In FIG. 10, end 704 of optical fiber 706 is retained such as by adhesive712 within an aperture 714 in a substrate holder 716.

Array 700 of optical emitters 702 comprises a semiconductor die includedin a module 722 comprising a substrate 724 having a substrate surface726 and a metallized cavity or well 728 containing optical transmitter720. Array 700 of optical emitters 702 is at an active major surface 728of die 720. On active major surface 728 is a representative electricalcontact 730, which serves a control input for controlling activation ofindividual emitters 702 of array 700. An arrow 732 represents light (notnecessarily visible light) from an emitter 702 of array 700 directedtowards optical fiber 706 end 704. Lenses may be employed in the opticalpath to capture light directed into waveguide end 704.

Optical transmitter die 720 includes a metallized back contact 734secured to and electrically connected to a metallization layer 736within cavity 728, and extending to a contact pad 738 on substrate 724surface 726.

For electrical interconnections, an HDI overcoat layer 740 includes anoptically transparent dielectric film 742 laminated over substrate 724surface 726 and active major surface 738, employing an adhesive layer744. Representative vias 746 and 748 are formed over contact pads 730and 738, and representative electrical conductors 750 and 752 comprisinga patterned metallization layer extend from vias 746 and 748 torepresentative module contact pads 754 and 756, respectively. Optionallya window (not shown) may be formed and polyimide 742 and adhesive 744layers over array 700 of emitters 702.

For alignment purposes, optical emitters 702 are individually energizedin a sequence, while the output signal at the other end 708 of opticalfiber 706 is monitored by receiver 710, to determine which emitter 702in the array 700 of emitters achieves the best optical alignment.Thereafter, for subsequent data communications the particular one of theoptical emitters 702 determined to achieve the best alignment isemployed.

Although a single optical fiber 706 is illustrated in FIG. 10, theinvention is applicable as well as to a multiple fiber situation. Insuch an embodiment, optical emitter array 700 and the individual opticalfibers are operated in essentially the same manner to identify which oneof the individual optical emitters 702 of array 700 achieves the bestalignment with each of the optical fibers. A different one of theindividual optical emitters 702 is so identified for optical datacommunication via each of the individual optical fibers. The inventionis thus employed in end-finding apparatus for fiber optic cables.

In a converse configuration, an array of optical receivers may beemployed in conjunction with an optical fiber. Such a configurationwould be illustrated in FIG. 10 by reversing the direction of arrow 732to indicate light coming from end 704 of optical fiber 706, andsubstituting for array 700 an array of optical receivers, such asphotodiodes. For actual alignment of the converse configuration, opticalfiber 706 and array 700 (of receivers) are operated by measuring theoutput signals of the individual receives of the array, to determinewhich one of the receivers provides the optimum optical path fromoptical fiber 706 end 704.

Likewise, in FIG. 10 optical receiver 710 may comprise an array ofoptical receivers, an identified one of which provides an optimumoptical path from end 70-8 of optical fiber 706. Thus, the embodiment ofFIG. 10 may be extended to a bundle of individual optical fibers with anarray of optical transmitter elements at one end and an array of opticalreceiver elements at the other end. For each of the individual opticalfibers, a particular one of the array of optical transmitter elementsand a particular one of the array of optical receiver elements areidentified which achieve the best alignment and accordingly the optimumoptical path.

While only certain preferred features of the invention have beenillustrated and described herein, many modifications and changes willoccur to those skilled in the art. It is, therefore, to be understoodthat the appended claims are intended to cover all such modificationsand changes as fall within the true spirit of the invention.

What is claimed is:
 1. A method for aligning an optical emitter and anoptical receiver for data communications, the method comprising:providing an array of optical receivers; positioning the optical emitterand the array of optical receivers with reference to each other toestablish an optical data communication path; energizing the opticalemitter and measuring output signals of the optical receivers todetermine which receiver in the array of optical receivers achieves thebest alignment; and for subsequent data communications, employing theoptical receiver determined to achieve the best alignment.
 2. The methodof claim 1, wherein energizing the optical emitter and measuring outputsignals of the optical receivers comprises manually energizing theoptical emitter and measuring output signals.
 3. The method of claim 1,wherein energizing the optical emitter and measuring output signals ofthe optical receivers comprises automatically energizing the opticalemitter and measuring output signals.
 4. The method of claim 3, furtherincluding periodically individually re-energizing the optical emitterand measuring output signals of the optical receivers to determine whichreceiver in the array of optical receivers achieves the best alignment.5. The method of claim 1, wherein one of the optical emitter and thearray of optical receivers is mounted on a plug-in circuit module andthe other of the optical emitter and the array of optical receivers ismounted on a backplane, and wherein positioning the optical emitter andthe array of optical receivers includes inserting the plug-in circuitmodule in the backplane.
 6. The method of claim 1, wherein the opticalemitter and the array of optical receivers are mounted on respectivemodules, and wherein positioning the optical emitter and the array ofoptical receivers includes stacking the respective modules.
 7. Themethod of claim 1, which further comprises: providing an opticalwaveguide having one end optically connected to the array of opticalreceivers such that optical signals presented to the other end of theoptical waveguide are directed to the array of optical receivers; andwherein positioning the optical emitter and the array of opticalreceivers with reference to each other comprises positioning the opticalemitter and the other end of the optical waveguide with reference toeach other to establish the optical data communication path.
 8. Anoptical coupling system for data communications, comprising: an opticalemitter; and an array of optical receivers positioned within a predetermined tolerance with reference to the optical emitter forestablishing an optical data communication path, one of the opticalreceivers providing the optimum optical path from the optical emitter.9. The optical coupling system of claim 8, wherein one of the opticalemitter and the array of optical receivers is mounted on a plug-incircuit module and the other of the optical emitter and the array ofoptical receivers is mounted on a backplane which receives the circuitmodule.
 10. The optical coupling system of claim 8, wherein the opticalemitter and the array of optical receivers are mounted on respectivemodules assembled into a stack of modules.
 11. The optical couplingsystem of claim 8, wherein the optical emitter and the array of opticalreceivers are located on facing portions of respective modules assembledinto the stack of modules.
 12. The optical coupling system of claim 10,which comprises an intermediate module having an array of opticalreceivers for receiving optical signals from an optical emitter on amodule on one side of the intermediate module, and another opticalemitter for directing optical signals to another array of opticalreceivers on a module on the other side of the intermediate module. 13.The optical coupling system of claim 8, which further comprises: anoptical waveguide having one end optically connected to the array ofoptical receivers such that optical signals presented to the other endof the optical waveguide are directed to the array of optical receivers;and wherein positioning the optical emitter and the array of opticalreceivers with reference to each other comprises positioning the opticalemitter and the other end of the optical waveguide with reference toeach other to establish the optical data communication path.
 14. Theoptical coupling system of claim 8, wherein the array of opticalreceivers comprises an application specific integrated circuit chip.